Laryngeal Mask Airway Device

ABSTRACT

The invention relates to a laryngeal mask airway device ( 1 ) for insertion into a patient to provide an airway passage to the patient&#39;s glottic opening, the device ( 1 ) comprising an airway tube ( 2 ), a mask ( 3 ) attached to the airway tube ( 2 ), the mask ( 3 ) comprising a body ( 4 ) having a distal end ( 5 ) and a proximal end ( 6 ), a peripheral inflatable cuff ( 7 ), and defining an outlet ( 8 ) for gas, the mask ( 3 ) being connected to the airway tube ( 2 ) for gaseous communication between the tube ( 2 ) and the mask, the distal end of the mask being ventrally displaced, relative to the proximal end.

The present invention relates to a laryngeal mask airway device.

The laryngeal mask airway device is a well known device that is usefulfor establishing airways in unconscious patients. U.S. Pat. No.4,509,514 is one of the many publications that describe laryngeal maskairway devices. Such devices have been in use for many years and offeran alternative to the older, even better known endotracheal tube. For atleast seventy years, endotracheal tubes comprising a long slender tubewith an inflatable balloon disposed at the tube's distal end have beenused for establishing airways in unconscious patients. In operation, theendotracheal tube's distal end is inserted through the mouth of thepatient, past the patient's trachea. Once so positioned, the balloon isinflated so as to form a seal with the interior lining of the trachea.After this seal is established, positive pressure may be applied to thetube's proximal end to ventilate the patient's lungs. Also, the sealbetween the balloon and the inner lining of the trachea protects thelungs from aspiration (e.g., the seal prevents material regurgitatedfrom the stomach from being aspirated into the patient's lungs).

Although they have been enormously successful, endotracheal tubes sufferfrom several major disadvantages. The principal disadvantage of theendotracheal tube relates to the difficulty of properly inserting thetube. Inserting an endotracheal tube into a patient is a procedure thatrequires a high degree of skill. Also, even for skilled practitioners,insertion of an endotracheal tube is sometimes difficult or notpossible. In many instances, the difficulty of inserting endotrachealtubes has tragically led to the death of a patient because it was notpossible to establish an airway in the patient with sufficient rapidity.Also, inserting an endotracheal tube normally requires manipulation ofthe patient's head and neck and further requires the patient's jaw to beforcibly opened widely. These necessary manipulations make it difficult,or undesirable, to insert an endotracheal tube into a patient who may besuffering from a neck injury.

In contrast to the endotracheal tube, it is relatively easy to insert alaryngeal mask airway device into a patient and thereby establish anairway. Also, the laryngeal mask airway device is a “forgiving” devicein that even if it is inserted improperly, it still tends to establishan airway. Accordingly, the laryngeal mask airway device is oftenthought of as a “life saving” device. Also, the laryngeal mask airwaydevice may be inserted with only relatively minor manipulation of thepatient's head, neck and jaw. Further, the laryngeal mask airway deviceprovides ventilation of the patient's lungs without requiring contactwith the sensitive inner lining of the trachea and the size of theairway established is typically significantly larger than the size ofthe airway established with an endotracheal tube. Also, the laryngealmask airway device does not interfere with coughing to the same extentas endotracheal tubes. Largely due to these advantages, the laryngealmask airway device has enjoyed increasing popularity in recent years.

U.S. Pat. Nos. 5,303,697 and 6,079,409 describe examples of prior artdevices that may be referred to as “intubating laryngeal mask airwaydevices.” The intubating device has the added advantage that it isuseful for facilitating insertion of an endotracheal tube. After anintubating laryngeal mask airway device has been located in the patient,the device can act as a guide for a subsequently inserted endotrachealtube. Use of the laryngeal mask airway device in this fashionfacilitates what is commonly known as “blind insertion” of theendotracheal tube. Only minor movements of the patient's head, neck andjaw are required to insert the intubating laryngeal mask airway device,and once the device has been located in the patient, the endotrachealtube may be inserted with virtually no additional movements of thepatient. This stands in contrast to the relatively large motions of thepatient's head, neck and jaw that would be required if the endotrachealtube were inserted without the assistance of the intubating laryngealmask airway device. Furthermore, these devices permit single-handedinsertion from any user position without moving the head and neck of thepatient from a neutral position, and can also be put in place withoutinserting fingers in the patient's mouth. Finally, it is believed thatthey are unique in being devices which are airway devices in their ownright, enabling ventilatory control and patient oxygenation to becontinuous during intubation attempts, thereby lessening the likelihoodof desaturation.

Artificial airway devices of the character indicated, are exemplified bythe disclosures of U.S. Pat. No. 4,509,514; U.S. Pat. No. 5,249,571;U.S. Pat. No. 5,282,464; U.S. Pat. No. 5,297,547; U.S. Pat. No.5,303,697; and by the disclosure of the UK Patent 2,205,499. Suchdevices with additional provision for gastric-discharge drainage areexemplified by U.S. Pat. No. 4,995,388 (FIGS. 7 to 10); U.S. Pat. No.5,241,956; and U.S. Pat. No. 5,355,879.

In general, laryngeal mask airway devices aim to provide an airway tubeof such cross-section as to assure more than ample ventilation of thelungs, and the designs with provision for gastric drainage have beencharacterized by relatively complex internal connections andcross-sections calculated to serve in difficult situations wheresubstantial solids could be present in a gastric discharge. As a result,the provision of a gastric discharge opening at the distal end of themask applicable for direct service of the hypopharynx has resulted in atendency for such masks to become bulky and unduly stiff, thus makingfor difficulty in properly inserting the mask. Moreover, undue bulk andstiffness run contrary to the requirement for distal flexibility fortracking the posterior curvature of the patient's throat on insertion,in such manner as to reliably avoid traumatic encounter with theepiglottis and other natural structures of the pharynx.

A number of problems have been experienced with all of these prior typesof device. For example, some prior devices seek to prevent occlusion ofthe airway outlet by parts of the patient's anatomy, such as theepiglottis, by the provision of bars and the like across the outlet.Although such devices function well in most cases, they can makemanufacturing more complex, and can affect the performance of devices inuse. This is especially so in devices formed from relatively rigidmaterials, like PVC, as opposed to the more traditional Liquid SiliconRubber (LSR).

In general, devices formed from materials such as PVC are attractivebecause they are cheaper to make, and can be offered economically as“single-use” devices. However, there are material differences in PVC andPVC adhesives, such as increased durometer hardness as compared to LSR,which affect how the devices perform in use. For example, it has beenobserved that for a given volume of air, an LSR cuff will expand to alarger size than a comparable PVC cuff. This superior elasticity allowsthe LSR cuff to provide an anatomically superior seal with reducedmucosal pressure. To close the performance gap, the PVC cuff must be ofreduced wall thickness. However, a PVC cuff of reduced wall thickness,deflated and prepared for insertion, will suffer from poor flexuralresponse as the transfer of insertion force through the airway tube tocuff distal tip cannot be adequately absorbed. The cuff assembly mustdeflate to a thickness that preserves flexural performance i.e. resistsepiglottic downfolding, but inflate so that a cuff wall thickness ofless than or equal to 0.4 mm creates a satisfactory seal. And where maskbackplates are formed from PVC, as well as cuffs, the fact that theincreased durometer hardness of PVC is inversely proportional toflexural performance (hysterisis) means that the flexural performance ofthe device in terms of reaction, response and recovery on deformation isinferior to a comparable LSR device.

The above described problems are particularly acute in devices whichincorporate an oesophageal drain. As mentioned above, in any such deviceregardless of the material from which it is formed, adding anoesophageal drain in itself adds greatly to complexity of manufactureand can also affect the performance of devices, in terms of ease ofinsertion, seal formation and prevention of insufflation. These problemscan be exacerbated still further if PVC or similarly performingmaterials are used. For example, the skilled worker will appreciate thatin terms of manufacture, the need to provide a drain tube which issealed from the airway, and which must pass through the inflatable cuffposes a particularly difficult problem. In terms of effects onfunctionality, the provision of a drain tube can cause unacceptablestiffening of the mask tip area and occlusion/restriction of the airwaypassage.

According to the invention there is provided a laryngeal mask airwaydevice for insertion into a patient to provide an airway passage to thepatient's glottic opening, the device comprising an airway tube, a maskattached to the airway tube, the mask comprising a body having a distalend and a proximal end, a peripheral inflatable cuff, and defining anoutlet for gas, the mask being connected to the airway tube for gaseouscommunication between the tube and the mask, the distal end of the maskbeing ventrally displaced, relative to the proximal end. It has beensurprisingly found that a ventral displacement of the tip makesinsertion of the mask much easier because the tip is presented at anoptimum angle as it tracks around the curvature of the airway anatomy.

It is preferred that the extent of distal displacement is from about 5mm to about 20 mm, and it is most preferred that the extent of distaldisplacement is about 10 mm. This has been found to be the optimumrange. It has been found that if the extent of displacement is toogreat, the device will not lie in the correct position at its maximumextent of insertion.

It is preferred that the body describes a substantially convex curve,from the proximal to distal end. It is further preferred that the maskbody comprises a plate, the plate having a dorsal side and a ventralside, the dorsal side being substantially smooth and having a convexcurvature across its width. It is also preferred that the dorsal surfaceof the airway tube corresponds in curvature to the curvature across thewidth of the plate. All of these expedients assist in making insertionof the mask easier.

The airway tube preferably comprises a relatively more rigid materialthan the mask body. Both the airway tube and the mask body preferablycomprise a plastics material.

The device may further including an oesophageal drain tube, and theoesophageal drain tube may be disposed on the ventral side of the body,in order to maintain a smooth profile on the dorsal side, to makeinsertion easier.

The invention will further be described by way of example and withreference to the following drawings, in which,

FIG. 1 is a dorsal three quarter perspective view of a device accordingto the invention;

FIG. 2 is a right side view of the device of FIG. 1;

FIG. 3 is a dorsal view of the device of FIG. 1;

FIG. 4 is a ventral view of the device of FIG. 1;

FIG. 4 a is a ventral view of a further embodiment of device accordingto the invention;

FIG. 5 is an end view, looking from the proximal towards the distal endof the device of FIG. 1;

FIG. 6 is an end view, looking from the distal towards the proximal endof the mask of the device of FIG. 1;

FIG. 7 is an enlarged view of the mask of the device of FIG. 1;

FIG. 8 is a dorsal view of the device of FIG. 4 a;

FIG. 9 is a longitudinal sectional view along line Y-Y in FIG. 8;

FIG. 10 is a side view, enlarged, of the device of FIG. 4 a;

FIGS. 11A to 11K are transverse sectional views along lines A-A to K-Kin FIG. 10;

FIG. 12 is an exploded dorsal perspective view of a device according tothe invention;

FIG. 13 is an exploded ventral perspective view of a device according tothe invention;

FIG. 14 is a dorsal three quarter perspective view of a device accordingto the invention;

FIG. 15 is a right side view of the device of FIG. 14;

FIG. 16 is a dorsal view of the device of FIG. 14;

FIG. 17 is a ventral view of the device of FIG. 14;

FIG. 18 is an end view, looking from the proximal towards the distal endof the mask of the device of FIG. 14;

FIG. 19 is an end view, looking from the distal towards the proximal endof the mask of the device of FIG. 14;

FIG. 20 is a dorsal three quarter perspective view of the device of FIG.14;

FIG. 21 is a view of section CC-CC in FIG. 20;

FIG. 22 is a view of section VC-VC in FIG. 17;

FIG. 23 is a proximal end view of a part of the device of FIG. 14; and

FIG. 24 is a distal end view of a part of the device of FIG. 14.

Referring now to the drawings, there is illustrated a laryngeal maskairway device 1 for insertion into a patient to provide an airwaypassage to the patient's glottic opening, the device 1 comprising anairway tube 2, a mask 3 attached to the airway tube 2, the mask 3comprising a body 4 having a distal end 5 and a proximal end 6, aperipheral inflatable cuff 7, and defining an outlet 8 for gas, the mask3 being connected to the airway tube 2 for gaseous communication betweenthe tube 2 and the mask, the distal end of the mask being ventrallydisplaced, relative to the proximal end.

In this embodiment the device 1 further comprises an oesophageal drain10, the drain 10 comprising a conduit 11 extending from an opening 12 atthe distal end 5 to a drain outlet 13 disposed to the outside of thepatient when the device 1 is in place, wherein the conduit 11 is formedintegrally in the material of the body 4.

As can be seen from the drawings, the device 1, in terms of overallappearance is somewhat similar to prior art devices, in that it consistsof the basic parts which make up most if not all laryngeal mask airwaydevices, i.e. an airway tube 2 and mask 3 which includes a body part 4,and a cuff 7.

For the purposes of description it is appropriate to assign referencenames to areas of the device 1 and accordingly with reference to FIGS. 2to 6, the device 1 has a dorsal side 14, a ventral side 15, a proximalend 16 (in a sense that this is the end nearest the user rather than thepatient) a distal end 17 and right and left sides 18 and 19.

Referring firstly to the airway tube 2, in the illustrated embodimentsthe tube comprises a relatively rigid PVC material such as a shore 90AColorite PVC moulded into an appropriately anatomically curved shape.The tube 2 has some flexibility such that if it is bent it will returnto its original shape. Although it is resiliently deformable in thisway, it is sufficiently rigid to enable it to assist in insertion of thedevice 1 into a patient, acting as a handle and guide. In thisembodiment the airway tube 2 does not have a circular cross-section asin many prior devices, but instead is compressed in the dorsal/ventraldirection which assists in correct insertion of the device 1, helpsprevent kinking, and assists in comfortable positioning for the patientas the shape generally mimics the shape of the natural airway. In thisembodiment each side 18, 19 of the airway tube 2 includes a groove orchannel 20 extending for most of the tube's length from the proximal todistal ends. These grooves 20 further assist in preventing crushing orkinking of the airway tube 2. Internally the grooves 20 form ridgesalong the inner surfaces of the sides 18 and 19.

Referring now to FIG. 13, which shows an exploded view of the device 1,it can be seen that the airway tube 2 includes a flared distal end 22with surfaces 22 a disposed to allow for attachment of the tube 2 to themask 3, conveniently by over moulding of the mask 3 onto the airway tube2. Thus, the airway tube 2 itself can form a pre-mould used in formationof the device 1, which substantially simplifies manufacturing. Ofparticular note is the airway tube's dorsal mould surface 23 (FIG. 13).This surface 23 is located at the flared distal end 22, and takes theform of a flat land extending between the outer dorsal surface 2 a andthe inner dorsal surface 2 b (FIG. 24) of the dorsal wall 2 c. Itincludes optional through holes 2 d to allow the over moulded back plate4 to lock onto the tube 2, as will be described later on. This featurehelps ensure a secure connection between the different materials makingup the airway tube 2 and mask 3.

A further feature of the airway 2 is the oesophageal drain tube 41. Thisdrain tube 41 is located within airway tube 2, extending centrallythrough it from one end to the other, and in this embodiment it isdisposed in contact with the inner surface 2 a of the dorsal wall 2 b ofthe airway tube 2, and bounded on each side by raised, smooth walls (notshown) which form a shallow channel through which it runs.

The proximal end of the airway tube 2 is provided with a connector 42,for connection of the device 1 to a gas supply and drain (not shown) asshown for example in FIGS. 12 and 13 and in section in FIG. 9. Theconnector 42 comprises a connector body 43, an optional bite block 44and a connector plug 45. The connector body 43 and bite block 44correspond in shape and dimension with the internal shape of theproximal end of the airway tube 2 such that they fit inside it. Theconnector body 43 has a perpendicularly extending peripheral flange 46which extends at one point on its circumference into a tab 47. Connectorplug 45 attaches to connector body 43 by adhesive or other suitablemeans applied to flange 46. The connector plug 45 comprises major andminor bores 48, 49 which both lead into a common atrium 50 at the distalend of the connector plug 45 where it attaches to the connector body 43.Drain tube 41 extends into and through minor bore 49, such that the boreof the airway tube 2 and the bore of the drain tube 41 are separatedfrom one another.

Turning now to the mask 3, the mask 3 consists of two parts, a body part4 often referred to as a back plate, and a peripheral cuff 7.

The back plate 4 is formed in these embodiments by moulding from a shore50A Vythene PVC+PU. This material is substantially softer and moredeformable than the material of airway tube 2.

Referring now to FIG. 23, the back plate 4 comprises a generally ovalmoulding when viewed from the dorsal or ventral directions, having asmooth dorsal surface 24, a formed ventral surface 24 a (FIG. 17), aproximal joining portion 24 b, and a distal tip 61.

The dorsal surface 24 has a convex curvature from one side to the other,corresponding to the curvature of the dorsal surface of the airway tube2, and longitudinally, the dorsal surface 24 is also curved, having acurvature beginning at the joining portion 24 b and extending withconstant rate of curvature toward the distal tip 61. As a result the tip61 is ventrally biased relative to the distal end of the airway tube, inthe assembled device 1, the extent of displacement of the distal tip 61being approximately 20 mm or 10 degrees, in order to produce a curvaturein the mask that is suited to the anatomy of the patient. This is shownschematically at X in FIG. 2. On insertion, this displacement of the tip61 assists the mask in “turning the corner” in the insertion path.

When viewed from the ventral side, the integrally moulded structures ofthe back plate 4 can best be seen (FIGS. 4,7,12,17). The precise shapeof the ventral side 24 a of the back plate is illustrated particularlyin the sectional views shown in FIGS. 11A to 11K and in the enlargedperspective view in FIG. 7. Referring to the exploded view shown in FIG.12, the convex curvature of the dorsal surface 24 of the back plate 4 ismirrored in a corresponding concave curvature on the ventral side. Thus,the ventral surface 24 a forms a shallow, elongate channel taperingtowards the distal tip 61. The channel is bounded by walls 26. The walls26 have correspondingly shaped, longitudinally extending convex outersurfaces 25. Each wall 26 extends longitudinally substantially theentire length of the back plate 4 from the proximal joining portion 24 btowards the distal tip 61. Each wall 26 also has a convex inner surface28, but rather than terminating at an angle normal to the channel floor,the curve of each wall 26 is continued, the walls curving back over thechannel and terminating in inwardly extending webs 27 (FIGS. 7 and 11).The inner surfaces 28 of the side walls 26 curve down to form the floorof the channel but do not meet, because the base or floor of the channelis bisected by a longitudinally extending, integrally moulded conduitwhich is an oesophageal drain tube 11 extending along it for its entirelength from joining portion 24 b to distal tip 61. Thus, it can be seenthat the channel has three longitudinally extending conduits on itsinner surface, the two open outer conduits 28 a which are minor gasconduits in the assembled device 1, and the central drain tube 11, whichforms a septum there between.

Referring now in greater detail to the drain tube 11, it will be seenthat the tube 11 has a sufficient diameter such that its upper wallsection 11 a, i.e. the wall section furthest from the floor of thechannel, is on a similar level with the inwardly extending webs 27 ofthe side walls 26. Furthermore, the upper wall section 11 a itself alsohas outwardly extending webs 30, which taper toward, but do not meet,the correspondingly tapered edges of the webs 27. Thus, the uppersurface 11 b of the upper wall section 11 a of the drain tube 11, andthe webs 27, 30, together define a surface 11 c shown schematically by adotted line in FIG. 11), below the level of which run all three conduits11, 28 a.

Referring now particularly to FIG. 7, it can be seen that although thedrain tube 11 extends the full length of the back plate 4 from itsproximal joining portion 24 b to distal tip 61, the conduits 28 a do notextend the full length of the back plate 4, but instead terminate abouthalf way along its length. The floors 31 of the conduits 28 a curvegently upwards as they extend towards the distal tip 61 of the backplate 4 until they terminate at a level approximately equal to the levelof the webs 27 and 30. In the embodiment shown in FIG. 4 a, these areasare hollowed out to form depressions 31 b.

As illustrated in FIG. 12 and FIGS. 21 to 23, drain tube 11 extends todistal tip 61, terminating in an opening 12. Thus, an end section 11 eof the drain tube 11 protrudes past the end of back plate 4. This endsection 11 e is provided with dorsal webbing 11 a which extends toeither side of it, and around it to form a hood or pocket 36 a whichencloses the end section 11 e around its circumference. The hood orpocket 36 a is attached to the distal end of the drain tube 11 aroundthe circumference 12 a of opening 12 (FIG. 22). This hood or pocket 36 ais integrally formed in the material of the back plate 4 at distal tip61. It completely surrounds and extends from the circumference of thedrain tube opening 12 and the joint therebetween is smooth. Asillustrated, the ventral extent of the hood is more limited than thedorsal extent, the dorsal extent being to about midway back towards theproximal end of the back plate 4. Referring to sectional views A-A andB-B in FIG. 11, it can be seen that the drain tube 11 is supported onits right and left sides, and on its dorsal surface, by perpendicularlyextending webs 62. These webs 62 are integrally formed, and extend backfrom the opening 12 to the point where the end section 11 e meets theextent of the back plate 4. In the illustrated embodiment the dorsalwebs 62 extend substantially perpendicularly from the drain tube, but ina preferred embodiment, they may extend to one side or the other, at anangle of less than 90 degrees.

The second part of the mask 3 is the peripheral cuff 7. The cuff 7 is inthis embodiment blow moulded PVC and takes the form of a generallyelliptical inflatable ring having a central aperture 7 a, a relativelydeeper proximal end 37 with an inflation port 38 and a relativelyshallower distal end 7 b tapering to a “wedge” profile 39. As will beappreciated, particularly from the exploded views shown in FIGS. 12 and13, the cuff 7 is integrally formed in one piece. The wedge profile isprovided such that the ratio of dorsal to ventral side surface areasfavours the dorsal side. Thus, when deflated the distal end 7 b of thecuff 7 will curl with bias from dorsal to ventral side.

In the assembled device 1, drain tube 41 is inserted into airway tube 2,such that it protrudes from proximal end 16. The connector 42 isattached to the airway tube 2 by inserting the connector body 43 andbite block 44 into proximal end 16. The parts are an interference fitand can be secured by adhesive. Plug 45 is attached to connector body 43via flange 46, such that drain tube 41 passes into minor bore 49,terminating at or adjacent its mouth. Thus it will be seen that theminor bore 49 is solely in fluid communication with drain tube 41, andthe major bore 48 is solely in fluid communication with the interior ofairway tube 2.

Airway tube 2 is attached to the back plate 4 conveniently byovermoulding the back plate 4 onto the already formed tube 2. Thus, thejoining portion 24 b of the back plate 4 is moulded onto the dorsal arcof the airway tube 2 (FIG. 13). Secure attachment is facilitated by thesurfaces 22 a, 23 which provide an increased surface area onto which themoulding occurs, and through-holes 2 d, into which back plate materialcan flow. Drain tube 41 is connected in fluid tight manner to integrallymoulded drain 11, as demonstrated by arrow Z (FIG. 13).

The cuff 7 is bonded to the back plate 4 as illustrated in FIGS. 12 and13 by inserting the wedge shaped distal end 7 b of the cuff 7 into thehood or pocket 36 a at the distal tip 61 of the back plate 4 such thatthe wedge surface 39 mates with the inner surface 36 b of the hood 36 a,and sections of the inner periphery of the cuff 7 mate with convex outersurfaces 25 of back plate walls 26. The cuff 7 is bonded into the hoodsuch that the space between the hood and the cuff is airtight and inthis embodiment the cuff is provided with a “pinch off” 40 (FIGS. 21 and22) putting the cuff 7 and hood 36 a into fluid communication so thatthe air space in the hood can also be inflated, in addition to the cuff7 itself. However the cuff 7 pinch off does not extend the entiredistance towards the distal tip of the cuff to prevent the pressure ofinflation occluding the opening 12. The proximal dorsal surface of thecuff is bonded to the ventral arc of the distal end 22 of the airwaytube 2. Thus, it will be appreciated that unlike in previous devicesincorporating oesophageal drains, in the invention the drain 11 does notpierce the cuff 7, making manufacturing simpler. Furthermore, in priordevices in which the drain pierces the cuff, the cuff must be securelyattached around the circumference of the drain tube at the distal tip.Such a secure attachment, for example with adhesive, can make the tiphard, and prevent the drain tube collapsing in the deflated, flatteneddevice, which is highly desirable to enable the mask to pass easilyaround the curvature of the anatomy. In addition, the acute curvature ofa drain tube to cuff joint would be highly susceptible to cracking. Inthe invention, these problems are avoided because the drain tube 11 isintegrally moulded with the hood 36 a, which in effect forms a second orminor cuff at the distal tip.

As will be appreciated, the airway of the device 1, which is the conduitthrough which gas is passed to the patient, is provided by the bore ofairway tube 2, which terminates at flared distal end 22. Flared distalend 22 defines, along with back plate 4 and cuff 7, outlet 8 for gaspassing from tube 2 into mask 3. Outlet 8 includes three routes by whichgas may pass into the mask, namely a main gas conduit 8 a (FIG. 6), andtwo minor gas conduits 28 a.

In use, the deflated device 1 is inserted into a patient in the usualmanner with devices of this type. As noted above, the relative rigidityof the airway tube 2 allows a user to grip it and use it to guide thedevice 1 into the patient, whilst the relatively softer, more compliantmaterial of the back plate means that the mask will more readily deformto negotiate the insertion path without causing damage to the anatomy,and will return to its optimum shape to ensure that a good seal isachieved at the furthest extent of insertion. The ventral displacementof the distal tip 61 relative to the join between the back plate 4 andairway tube 2 further enhances ease of insertion, because the distal tip61 is thereby presented at the optimum angle to negotiate the “bend” inthe insertion path. In devices formed from relatively rigid materialssuch as PVC, as opposed to the often used LSR these features areparticularly important in easing insertion and providing for an enhancedseal.

Referring now to the features of the moulded back plate 4, it will beseen that by providing drain tube 11 integrally moulded in the materialof the back plate 4, problems of mask stiffness and difficulty ofmanufacture in prior designs caused by the presence of a separate draintube bonded in place with adhesive can be mitigated.

Moreover, with the back plate 4 of the invention, the combination of thecentrally located drain tube 11 and minor gas conduits 28 a assist insolving the problem of occlusion of the airway by parts of the patient'sanatomy. The minor gas conduits 28 a can be thought of as “nostrils”through which gas may continue to pass into the patient even if the mainoutlet 8 a becomes occluded by, for example the patient's epiglottis, asthe epiglottis will rest upon the septum provided by the drain tube 11.As illustrated particularly in FIGS. 11I and 11J the webs 27, 30 form apartial closure over the conduits 28 a, to assist in preventingstructures such as the epiglottis from falling into and blocking theconduits 28 a, and also to make the back plate 4 more resistant tolateral compression. It will be appreciated that in this embodiment, thedrain 11 forms a convenient septum between the conduits 28 a, however,in devices with no oesophageal drain, a solid septum could simply beformed in the material of the back plate by moulding. In addition, alarger number of conduits 28 a could be provided.

Thus, it can be seen that the above described embodiments address theproblems of prior art devices in novel and inventive ways.

1. A laryngeal mask airway device for insertion into a patient toprovide an airway passage to the patient's glottic opening, the devicecomprising an airway tube, a mask attached to the airway tube, the maskcomprising a body having a distal end and a proximal end, a peripheralinflatable cuff, and defining an outlet for gas, the mask beingconnected to the airway tube for gaseous communication between the tubeand the mask, the distal end of the mask being ventrally displaced,relative to the proximal end.
 2. A device according to claim 1, whereinthe extent of distal displacement is from about 5 mm to about 20 mm. 3.A device according to claim 2, wherein the extent of distal displacementis about 10 mm.
 4. A device according to claim 1, the body describing asubstantially convex curve, from the proximal to distal end.
 5. A deviceaccording to claim 1, the mask body comprising a plate, the plate havinga dorsal side and a ventral side, the dorsal side being substantiallysmooth and having a convex curvature across its width.
 6. A deviceaccording to claim 5, the airway tube having a dorsal surface, thedorsal surface of the airway tube corresponding in curvature to thecurvature across the width of the plate.
 7. A device according to claim1, the airway tube comprising a relatively more rigid material than themask body.
 8. A device according to claim 1, further including anoesophageal drain tube.
 9. A device according to claim 8, theoesophageal drain tube being disposed on the ventral side of the body.